This function returns a list of ASCII digits that prefix a list, so collect_digits("1234.0") returns "1234". And now one more "suppose": suppose that one time we decide that we really need to process the result of collect_digits backward, so we do this:

reverse(collect_digits(List))

The question is, can the compiler detect that there's a double reverse? In theory, the last reverse could be dropped from collect_digits in the generated code, and each call to collect_digits could be automatically wrapped in a call to reverse. If there ends up being two calls to reverse, then get rid of both of them, because it's just wasted effort to double-reverse a list.

With lists:reverse as a built-in, this is easy enough. But can it be deduced simply from the raw source code that reverse(reverse(List)) can be replaced with List? Is that effort easier than simply special-casing the list reversal function?